Drying system and method



May 11, 1937. D, D PEEBLES 2,080,059

DRYING SYSTEM mu: METHOD Filed Sept. 24, 1932 INVENTOR. flay/'0 0. Peeb/as A TTORNE YS.

' increaslngly less eflicient.

Patented May 11, 1937 u'Nl'uED STATE s PATENT OFFICE acaausc DRYING SYSTEM AND METHOD David D. Peebles, Eureka, Calif.

Application September 24, 1932, Serial No. 634,738

3 Claims.

This invention relates generally to systems and methods for the drying of various materials, particularly materials which in the past have been dried upon heated drums.

In the past many industrial processes have made use of drum type dryers for recovering solid components of fluid material in dry form. Such dryers commonly utilize a steam heated drum upon theouter surface of which a layer of the fluid material is applied. In operation, I have found that such dryers are characterized by f airly eilicient evaporation of moisture, until the material contains in the neighborhood of say 40 to 60% solids, after which the drying action is This is due to the fact that it is more difficult to drive off moisture from the denser material, because ebullition is retarded and heat conductivity is reduced. In view of this characteristic if it is desired to carry the moisture content down to say one or two percent, drum type dryers become relatively ineiiicient, and ii a considerable plant capacity is desired, a large number of such dryers must be employed at great expense.

It is an object of the present invention to devise a drying system and method which will make use of a drum type dryer only to the extent to which such, dryers are relatively eiiicient, and which will finish the drying of the material in an efllcient and simple manner.

A further object of the invention is to provide a system and method of the above character which will materially reduce the time required for drying materials in plant operations, which will have relatively high capacity compared to its size, and which will result in a relatively uniformly dried product.

Further objects of the invention will appear from the following description in which the preferred embodiment'of my invention has been set forth in conjunction with the accompanying drawing. It will be understood that the appended claims are to be accorded a range of equivalents consistent with the state of the prior art.

My system as diagrammatically illustrated in the drawing consists of a drum type dryer III, in conjunction with a finishing dryer II. An amount of drying is carried out by the drum type dryer in consistent with the range for which this dryer is relatively eiilcient and to an extent which will enable removal of the material, while the remainder of the drying, down to say 1 to 2% of moisture, is accomplished in the finishing dryer ii. The extent of drying in the drum type dryer will obviouslydepend somewhat upon the character of the material being treated.

'I'he'drum type dryer Ill consists of a rotatable drum I 2, adapted to be heated by steam. The supply of material in fluid condition'to be dried is indicated at I3, and this material is spread upon the heated periphery of the drum I2, by applicator I4. A knife edge, brush or other scraping means is indicated at I6, for removing the semi-dried material from the drum, and for delivering it into suitable conveying means II.

The finishing dryer I I consists of a chamber I8, which can be cylindrical in shape, and which is provided with inflow and outflow conduits I9 and 2|. Movements of gas thru chamber I8 is maintained by connecting outflow conduit 2i, to the inlet of a blower 22, the discharge conduit 23 of which may lead to further apparatus, as for example a bag filter. The drying gas flowing in thru conduit l9, which may be air, is heated to a suitable elevated temperatureby suitable means such as a heater 24. Conveyor I1 is arranged to deliver the semi-dried material into conduit I9, thru the conduit connection 26, so that this material is conveyed by the rapidly moving stream of air and delivered into the chamber III for further treatment. It will be noted that the connection between conduit I9 and chamber I8 is arranged tangentially, to aid in causing currents of air within the treatment chamber I8 to swirl about a central axis.

In order to maintain a sufficient period of contact between the material being dried and the drying gas, I preferably provide recirculation means in conjunction with chamber I 8. This recirculation means can consist of a blower 21, having its inflow conduit 28 connected tangentially to chamber I8, and having a similar tangential connection for its outflow conduit 29. The tangential connection between blower 21 and the treatment chamber further aids in maintaining swirling currents of dryinggas in which the material is suspended. If desired the flow of air can be maintained by a blower interposed in conduit l9, in place of or supplemental to' blower 22. I I

Outflow conduit 2| connects with chamber l8 thru the upper wall of this chambenand in substantial alinement with the vertical axis of the swirling currents of gas. Since the temperature of gas leaving thru conduit 2I may at times be sufficiently high to burn a bag type filter, I preferably provide suitable cooling means such as a conduit or pipe 8|, by means of which regulated quantities of cool air can be introduced into to admit cool air.

Operation of my system and method will be described with respect to the drying ofmagnesium basic carbonate, because my invention aiiords a practical'and novel solution of the problem of drying this material as produced in industrial processes. ing in this case oi a suspension of magnesium basic carbonate in water, is supplied to the drum dryer Ill a't l3. As the material is delivered from the drum dryer to the conveyor ll, it contains in the neighborhood of from 50 to 60% or more solids. Such material is sumciently dry that it can be conveyed pneumatically thru conduit Ill, and will be suspended by the swirling currents of drying gas in chamber l8 without atomization. In chamber II the material is maintained in suspension in contact with the drying gas or hot air, until the moisture content has been reduced to from say 1 to 2%, after which the dried particles are carried pneumati cally thru conduit 2| and delivered to conduit 2!. Within chamber ID the material is not only contacted with the drying gas, but thereis also an automatic classifying action. Particles which are not sufliciently dried for delivery thru conduit 2|, tend to 'remain.within this chamber, and also tend to progress downwardly and to be redelivered by blower 21 to the upper portion of the chamber. .Thus all particles of the basic carbonate are subjected to the drying gas for a sufliciently long period until the moisture content has been reduced to the desired value, after which they are delivered to conduit 2|.

It is evident that my system and method has many desirable characteristics. .The drum type dryer is utilized only for an efilcient range of operation, thus making possible relatively high plant capacity with comparatively few dryers of this type. For example it has been found that two drum type dryers, utilized in my system, will handle substantially the same capacity as five or more drum type dryers utilized as in the past in such a manner as to complete the drying of the material. -My finishing dryer II is relatively inexpensive andsimple to operate, compared to the additional drum type dryers which The fiuid material, consistwould be required to complete the drying, ii my system were not employed. Likewise because of the use of my finishing dryer in conjunction with a drum type dryer, I need only utilize suflicient air to'maintain the particles of material in the treatment chamber IS in suspension, and special rotary atomizers need not be employed.

I claim:

1. In a drying system, a desiccating chamber, means for introducing astream of-drying gas tangentially into said chamber, means for entraining divided material to be desiccated into said stream of gas prior to introducing the gas into the chamber, means including an external blower forming a recirculation path for continuously removing a portion of the gas and en trained material from the lower portion of said chamber and for re-introducing the same back into the upper portion 01' the chamber, and means for continuously removing gas together with'entrained and desiccated material from said chamher, said last means including an outflow conduit having an open inlet end located near the upper end of the central axis of the desiccating chamber. I

2. In a drying system, a desiccating chamber, means for introducing a stream of drying gas tangentially into said chamber, means for entraining divided material to be desiccated into said stream of gas prior to introducing the gas into the chamber, means including an external blower forming a recirculation path for continuously removing a portion of the gas and en-' trained material from the lower portion of the chamber and for introducing the same back into the upper portion of the chamber in a tangential direction, and means for continuously removing .gas together with entrained and desiccated material from'the upper portion of said chamber, said last means including an outflow conduit having ,an open inlet end located near the central axis of the chamber.

3. In a drying method characterized by the use of a desiccating chamber, introducing a stream of drying gas tangentially into said chamber, feeding divided material to be desiccated into said stream of gas and conveying the material by the stream of gas into the chamber, continuously diverting a stream of gas from one end portion of the chamber, adding kinetic energy to the gas so diverted and returning the same back into the other end portion of the chamber, and continuously removing gas together with entrained and desiccated material from a localized region 

